1. Field of the Invention
The present invention relates to a sheet folding apparatus, a sheet folding method and an image forming apparatus wherein the sheet folding apparatus and the sheet folding method are intended to ensure that a sheet with image recorded thereon, ejected from an image forming apparatus, is folded in two or more.
2. Description of Related Art
The prior art disclosed so far includes a sheet folding apparatus consisting of a copying machine as an image forming apparatus, having a function of folding sheets with image recorded thereon, and a post-processing apparatus having a function of folding and binding the sheets.
Further, a sheet folding apparatus for folding one or a few sheets of sheets in two or three is also utilized as an apparatus for creating a sealed document such as postal matter.
In the sheet folding apparatus disclosed in the Japanese Application Patent Laid-Open Publication No. 2002-284444, two or more folds are formed on a sheet of sheet subjected to image forming processing, using a plurality of pairs of folding rollers and a sheet leading end stopping member, and Z-shaped fold processing is performed. This sheet folding apparatus stops the leading edge of the sheet having been transported, by hitting it against a sheet leading edge stopping member. The deflected portion of the sheet caused by this sheet leading edge stopping member is placed between a pair of folding roller, thereby forming a fold.
The post-processing apparatus disclosed in the Japanese Application Patent Laid-Open Publication No. 2002-60127 is equipped with a first folding section and a second folding section. When the twofold mode is selected by a selection section, the first folding section is actuated to fold the sheet into two and to eject it. When the threefold mode is selected by the selection section, the first folding section is actuated to fold the sheet. Then the second folding section is operated to fold the sheet again, whereby the sheet is folded into three and is ejected. The first folding section produces the first fold using the first pair of rollers and folding knife, and the second folding section uses the produces the fold by allowing the deflected portion of the sheet crated by the sheet leading edge stopping member, to be inserted between the second pair of rollers.
According to the sheet folding apparatus described in the Japanese Application Patent Laid-Open Publication No. 2002-284444, the fold produced on the sheet is displaced by the difference in the thickness and strength (stiffness) of the sheet in some cases.
In the post-processing apparatus shown in Japanese Application Patent Laid-Open Publication No. 2002-60127, when a plurality of sheets of sheets are stacked one on top of another into a bundle of sheets to produce a fold thereon, the outside sheet in contact with the outer peripheral surface of the folding roller is first caught between the folding roller, and the outside sheet is folded in the state displaced from the inside sheet. This has created a problem in this prior art.